FIX: remove bash-isms from igprof shell script

Ubuntu uses `/bin/dash` instead of `/bin/bash` as the standard shell. Since `src/igprof` uses `#!/bin/sh` as shebang and utilizes bash-isms in the script it does not run under ubuntu without manual intervention.
In detail `src/igprof` was using bash-arrays to tokenize an input string for the `-fp*` flag. This pull request replaces the bash-isms by utilizing the `cut` utility.
Additionally the script used `==` to compare strings, which also failed in certain conditions.